1. Field of the Invention
The present invention relates to a developing device in an image forming apparatus of an electronic photography process for a copying machine, a printer, etc.
2. Description of the Prior Art
In an image forming apparatus in electronic photography process, a developing device for image forming related to electrostatic latent images of document images imaged on a photosensitive drum by adsorbing a developing agent from a developing roller which rotates contiguously thereto utilizes various means, depending upon the kind of developing agent and the developing system. However, it is general that developing is carried out at a developing treatment unit formed between the photosensitive drum and the developing roller as described above. At this time, it is important that the interval or contact pressure between the developing roller and the photosensitive drum does not fluctuate, and excessive fitting contact pressure must not be given to the photosensitive drum.
FIG. 4 shows a developing device disclosed in the Japanese Patent Publication No. SHO 63-67185 as one of the examples of conventional units for forming a developing device as described above. A developing roller 5 disposed in the vicinity of a photosensitive drum 1 is integrally constructed with a hopper 8 which accommodates a developing agent 9 and is suspended and supported as developing unit 4, which is confronted to the photosensitive drum 1, by a suspending member 11 with a pin 10 used as axis. The developing unit 4 is constructed so that it can be pressed to the photosensitive drum 1 by its self-weight and energizing springs 12, 13 and is given transmission of drive force by engagement of a gear 3 fixed at the photosensitive drum 1 and a gear 6 of the developing roller 5.
In the above conventional construction, the developing unit 4 which is suspended and supported is likely to generate torque in the direction of keeping the developing unit 4 away from the development treatment portion due to rotational drive to such a degree as the larger the torque becomes because there is a distance between the supporting axis and the drive transmission portion to which drive force is transmitted, and there is such a problem as the interval of the developing unit consisting of the developing roller 5 and the photosensitive drum 1 fluctuates. As the interval between the photosensitive drum 1 and the developing roller 5 is kept away, the developed image is made to be white blanked, and on the other hand, as a compression force by which the developing roller 5 is charged to the side of the photosensitive drum 1 in order to suppress this torque of keeping away is strengthened, excessive load is given to the photosensitive drum 1 to damage the photosensitive body, thereby a problem which produces strain or distortion at the developing unit 4 is caused to be present.